The HIS 4890 Turbo uses factory overclocked settings to squeeze more juice from the new ATI Radeon HD 4890 graphics chip. As the HD 4890 is heavily based on the HD 4870 we'd better start there.

A basic HD 4870 is clocked with a core speed of 750MHz core and either 512MB or 1GB of GDDR5 memory that runs at an effective speed of 3600MHz. You can expect to pay £160 for an HD 4870. The new HD 4890 has revised power management to allow the higher clock speeds with a reference core speed of 850MHz and memory that runs at 3900MHz. The HD 4890 is only available with 1GB of memory and you can expect to pay £199 for ATi's latest and greatest graphics card.

HIS has added to the excitement by clocking the Turbo at 900MHz/4000MHz, which is a handy chunk of extra speed, but the price has also risen to a penny under £240.

Get the latest Dell Coupons and other computer coupons at CheapStingyBargains.com.

In appearance the Turbo looks identical to both a regular HD 4890 and also to the HD 4870, as it is a double-slot design that uses ATI's blower cooler. Internally the RV790 chip in HD 4890 is very similar to the RV770 used in HD 4870, as both chips have 800 stream processors, use 956 million transistors on a 55nm fabrication process and connect to the GDDR5 memory with a 256-bit controller.

The RV790 has been updated to improve power management with the result that the idle power draw has been reduced from 90W for the HD 4870 to 60W for the HD 4890, although the maximum power draw under load has increased from 160W to 190W.

We plugged the HIS 4890 Turbo into a Core i7 test PC and the results were impressive, with a score of 11,737 marks in 3DMark Vantage. We played Far Cry 2 at an HD resolution of 1,920 x 1,080 with maximum quality settings and 2x Anti Aliasing and saw an average 57 frames per second.

That's truly impressive so we were excited to see whether our factory overclocked Turbo could run even faster. We cranked up the speed from 900MHz/4000MHz to 970MHz/4500MHz but the results were nothing like as impressive as we had expected. The 3DMark Vantage score rose by a tiny amount to 11,984 marks and the frame rate in Far Cry 2 rose by three frames per second.

Perhaps this is evidence that HIS has overclocked the HD 4890 to give a slug of extra performance without heading to ridiculous extremes that would only deliver rapidly diminishing returns.

The ATI Radeon HD 4890 makes impressive advances over the HD 4870 but you pay a premium for the privilege of the extra speed. Unfortunately you pay HIS a further premium for its factory overclocked Turbo model and, while the results are similarly impressive, they are also uncomfortably expensive.